It depends on what your trait is. Let's say that your trait was tongue roller. Rolling your tongue is dominant over non-tongue rollers so we would use R for Rolling your tongue. For the recessive trait, non-tongue roller, we use the same letter as the dominant trait except it is lowercase. So non-tongue roller would be r.
The recessive trait isn't present when the dominant form of the trait is there. Whenever a trait is dominant trait is present it ALWAYS takes over the recessive one. the law of Dominance
A trait that masks another trait is called dominant, or a dominant trait.
Recessive trait
The trait that is masked is recessive. The trait that does the masking is dominant.
The dominant trait masks the recessive trait.
If the gene is governed by a dominant and recessive allele, then if the dominant allele is present, the dominant trait will be expressed. If both alleles are recessive, then the recessive trait will be expressed.